To provide a sliding door overturn prevention device for preventing the overturn of a sliding door by preventing the lower end of a sliding door from moving in a direction orthogonal to a lower rail section.

An upper rail section 6 and a lower rail section 7 are respectively installed at an upper frame section 4a and a lower frame section 4b of a sliding door frame 4, and the upper end and lower end of a sliding door (first sliding door 12 and second sliding door 13) are respectively supported by the upper rail section (6) and the lower rail section (7) so as to be movable, and an overturn regulation member (sliding door overturn prevention components 20 and 21) for regulating the lower end of the sliding door (first sliding door 12 and second sliding door 13) from moving in a direction orthogonal to the lower rail section (7) is disposed on a side of the lower rail section (7).